Questions tagged [fft]
FFT is an acronym for Fast Fourier Transform. Use this tag for FFT-related questions. Try to also select a specific chip or software tag when possible.
218
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Discrepancy Between Bode Plot Predictions and FFT Output for Higher-Order Low Pass Filters on a 10 kHz Square Wave
I have conducted an experiment where a 10 kHz square wave is input through low pass filters of 1st, 2nd, 3rd, and 4th orders. After passing the square wave through these filters, I observed the FFT (...
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FFT on my oscilloscope is not detecting a peak which is a peak
I am having a strange problem and it's due to that lack of my info about signals.
I examined a PWM output from my MCU under sds1104x-e oscilloscope which is 656KHZ with a duty cycle of around 45.5% ...
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How to plot the FFT in Ltspice?
I'm new in Ltspice and I wonder how to plot the FFT of R1? I just failed to find such a tutorial and I'm sorry for such a stupid question. Thanks for your teaching!
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FFT is not showing noise
I have current values and respective time.
There is noise in the signal. But when I am calculating FFT, it is not showing
I have recorded the values at every 5ms.
below is my code:
...
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VHDL my FFT design doesn't work at larger N-point
I built an FFT module for an 128-point FFT in VHDL. When I use the same principle for 8-point fft or 16-point fft (ofcourse then the file must be altered for less stages and different twiddle factors),...
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How do you find Image Rejection Ratio from doing FFT on ADC samples?
I'm trying to understand a particular code written by a former employee for measuring performance of an RX chain in a transceiver. I have to measure IRR(Image Rejection Ratio).
Certain input RF ...
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What two laws of harmonics are demonstrated here? [closed]
I clipped the top and bottom of a sine wave at exact reciprocal angles (73.73159173° to 106.2684083° and 253.73159173° to 286.2684083°) to prevent the creation of even (red) harmonics (by being ...
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How would you compute Fourier transform of a real world signal where the signal keeps getting updated (not a static one)?
A very naive question: How do we use Fourier transform for real world signals - for which you have the information only up to the present instant (and the present time keeps moving continuously)?
The ...
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Error with arduinoFFT library
I'm trying to use the arduinoFFT library (https://github.com/kosme/arduinoFFT) with my ESP32. I made a basic program just to see if the FFT is done correctly. The problem is that I can't compile the ...
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How to achieve coherent sampling in practice
In the context of measuring a sinusoidal source with an ADC, coherent sampling (i.e. capturing an integer number of periods) allows the use of a rectangular window without spectral leakage.
How does ...
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Fourier Transform of Voltage Readings
I am working on developing a Fourier transform for voltage readings. The goal is to determine voltages at different frequencies (frequency domain). I am taking readings at 100Hz and am measuring both ...
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FFT analysis in LTSpice is giving wrong results during partial execution of time domain simulation (Details in body)
In LTspice, while computing FFT using waveform window (View-> FFT), the results seems to be wrong if FFT is computed after partial execution of simulation ( eg: if simulation is paused in between)...
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Converting beam index to angular units
Assume I have a MIMO channel matrix \$H\$ of dimension [\$N_r\$ \$N_t\$ \$N_f\$] where \$N_r\$ are the number of antennas at the receiver, \$N_t\$ the number of antennas at the transmitter, and \$N_f\$...
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Data-set creation and signal processing
I'm taking a digital signal processing course and I have a project to create a data set with a microcontroller and process it for this course. I want to count only dog bark for example not dog growl. ...
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Propagation phenomena in cables
I have came across the propagation phenomena that takes place when we have a source and a load connected through a cable. We have an impedance mismatch and hence a propagation phenomena.
So what I did,...
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Sampled 100 Hz sinusoidal signal from Hall sensor shows 10 Hz sidelobes when sampled at 500 Hz
I am working on a project where I need to measure an oscillating magnetic field that oscillates at a frequency of 100 Hz. For this reason, I am using a Hall sensor. I programmed the Hall sensor to ...
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Battery-powered FFT project
I want to use FFT on a STM32F401C01CCU6. I chose this microcontroller because everyone says the F4 series is good at signal processing.
I want to make a project that will work with a battery; I am not ...
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In LTspice, why doesn't the FFT plot update after a simulation?
I'm using LTspiceXVII (17.0.35.0). I run a simulation and make an FFT plot. Then I change a parameter and the time waveform updates, but the FFT plot doesn't update. I have only been able to see ...
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Second-order LPF not filtering correctly
I am trying to implement a 2nd-order Butterworth low-pass filter with a cut-off frequency of 9 kHz.
As an input I was using a square wave of 12 kHz. My op-amp rails are 0 and 5 V. The sqaure wave has ...
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Can I directly use an oscilloscope's FFT function for EMI measurement?
The latest oscilloscopes with FFT and real-time functions are very useful for EMI debugging with a near-field probe, but why can't we just use them for the far-field EMI scan? EMI receivers are much ...
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How to have a wider spectrum of FFT at LTspice?
I've used the FFT analysis tool to see the spectrum of DM and CM EMI noise in the range of 150K to 30MHz.
But the analysis stops at about 3MHz automatically and there is no option to set the max and ...
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Filtering when collecting a signal in the time domain
I reconstructed a signal (from simulations) in the time domain from t ~ 0.01 to 2000 s. I do this by calculating "modes" or constants for the system that I'm studying that should be exact ...
user314730
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How to remove aliasing effects?
I collected data in the time domain and then calculated the FFT to see how it looks in the frequency domain. Since the signal isn't band-limited, I think I have aliasing and there are features at high ...
user314730
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How do you bandlimit a continuous-time signal?
I wish to avoid aliasing as a result of taking the FFT of a signal. The signal isn't band limited. My understanding is that I should band limit the continuous-time signal first. How do I do this?
EDIT:...
user314730
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Range Profile in Radar System
I am slightly confused on the range profile I am obtaining from my SCFW radar dataset. I am understanding of how fftshift works in shifting positive and negative frequency components to be centered ...
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238
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Generating a sinewave on Matlab with specific harmonics [closed]
I need to generate a sinewave on Matlab so I can use the generated values, I need 1000 samples per cycle for grid simulation using micro-controller. I was able to generate a pure sinewave and it is ...
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What is the unit of power spectral density?
I have an oscilloscope data, I did plot in time domain, so that unit is in volts (Y axis). After that I took FFT. So now what will be the unit in Y axis?
If I will do 10 log 10 (y axis) can it is ...
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Creating a Range Profile
I am relatively new to the radar/signal processing community. However, my team has been struggling in developing a range profile in our programming. Here are the details for a NI LabVIEW forum I ...
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How to get audio frequencies from mems microphone in PC oscilloscope
I'm fairly new to electronics/signal processing and I'm stuck on trying to obtain frequencies from an Adafruit SPW2430 MEMS microphone. I tried plugging the microphone to a Hantek 6022BE PC ...
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Generating and measuring a sine wave with THD below -80dB
For an experiment I need to generate a sine wave which has a THD below -80dB. I would like to do that using a band-pass filter connected to a function generator because the output of the function ...
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Cross-correlation in time or frequency domain (FPGA)
I need to compute the complex cross-correlation between two signals a and b and the take only the maximum value of the cross-correlation, regardless of the lag time where this occurs. I can do it ...
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LTSPICE: Dirty gate voltage and low gain - Hartley oscillator using MOSFET
I'm designing a Hartley oscillator using a MOSFET, but I have some issues. I've chosen L1 as 3 times L2 to obtain a gain of 3, however, it's more like 2.4.
First of all, I can't understand why the ...
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.four plot FF/t LTspice
I am trying to plot an FFT in LTspice using a .four command and the spice error log directly without using the FFT on LTspice (right click + view + FFT once the ...
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What determines amplitude resolution of oscilloscope FFT?
I am studying my oscilloscope's FFT measurement capability (Rigol DS1054Z. Links to datasheet and user guide), and do not understand what determines the amplitude resolution capability of the FFT ...
user283168
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What is happening when a signal is acquired at exactly Nyquist frequency?
So I am doing some some simulations with 1V sinusoidal signals, and a 1 second acquisition at sampling frequency of 100 kHz.
Now I am slowly increasing the frequency of the sinusoidal signal. Trying 1 ...
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Windowing FFT: spectral leakage vs ENOB
I am using Cadence to perform full speed testing of a 4-bit SAR ADC using the FFT and non-coherent sampling.
I've obtained the ENOB and the spectra of the output signal using first the rectangular ...
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Why am I getting linear phase?
I'm trying to plot the phase of Fourier transform of the function below:
\begin{gather*}
x[n] = 2e^{-0.9|n|} \: \: n \in [-5,5]\\
x[n] = 0 \:\: n \notin [-5,5]
\end{gather*}
which is equal to the ...
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Numpy giving the wrong Fourier transform of sine functions
I'm using numpy's FFT to calculate the Fourier transform of \$\cos(\omega_0t)\$ and plot it. By using the definition we can derive its Fourier transform as below:
\begin{equation}
X_3(j\omega) = \pi (...
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How can we obtain the input signal given the output signal and transfer function?
From an electrical circuit, I have the transfer function as:
$$
H(s) = \frac{R}{sRC + 1}
$$
\$V\$ is the output and I is the input so we can write:
$$
V(s) = I(s) H(s)
$$
or
$$
V(jω) = I(jω) H(jω)
$$
...
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Reason for frequency steps shown in Simulink FFT analysis tool
While using the FFT in Simulink tool, I have observed that if more number of cycles are selected then frequency steps in which harmonics percentage is shown is also divided accordingly.
For example:
...
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How to use DFT to find harmonic content of an AC waveform?
I am kind of new to this coding and simulation environment. For my first project I need to take samples of current signals from power line and find out the harmonic contents using DFT. I haven't done ...
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Voltage RMS and Voltage Spectral Density from ADC Sample are Not Consistent
I have time series data from a 100 MS/s ADC, and I would like to calculate the RMS noise and the voltage spectral density (VSD), and see consistency between the two.
I'm using a 16-bit ADC, and the ...
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Uniform circular array (UCA) beamforming using FFT
As far as I know, conventional beamforming using FFT can return a range-angle map. However, this only works with a uniform linear array (ULA).
I'm wondering if the same approach works for UCA. I guess ...
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What should be my sampling frequency for a peak detector output where it is extremely important for me to capture the first time the peak occured?
Following is the output of the peak detector:
The amplitude is not important to me, however the time when the peak occurs is extremely important. So my microcontroller will have an algorithm like ...
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OFDM IDFT implementation
i have some doubts with the implementation of the IDFT in OFDM systems.
The question concerns the expression of the IDFT of the OFDM signal.
During the symbols period \$T_s\$ we have the following ...
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How to calculate subcarriers bandwidth and cyclic prefix length in an OFDM using the IFFT
I'm trying to understand how OFDM works thanks also to the Simulink OFDM block.
Now, I have understood that the OFDM modulation "convert" a faster bit rate using a certain bandwidth into a ...
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How to convert amplitude (V) to dB (V^2/Hz or V/sqrt(Hz) or V?)
I took the FFT of a signal and am currently plotting amplitude (V) vs. frequency (Hz). I'd like to change the Y-Axis units to dB. How would I go about doing this? What would be the units?
It is from ...
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How to detect dog bark? [closed]
I need to design a small dog bark detector. It should be as cheap as possible (10$ manufactured unit.) It should be accurate because it can be used anywhere in noisy places.
The aproach I am ...
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What happens if the signal frequency exceeds the sampling rate?
As the title states, I was wondering what happens to the frequency contents of the sampled signal of a pure sinusoidal signal that exceeds the sampling rate.
I am familiar with the shannon theorem and ...
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FFT analysis of summed signal in LTSpice
I know that simulating FFT analysis of current/voltage across a single element via LTSpice is quite straightforward. I have simulated the summation of three distinct currents in the time domain. I'd ...
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